Hi,
note that the a axis units are degrees....

Craig

Hi,
if you want .005 resolution on a 4 inch diameter:

.005/ 2(radius) =0.0025 radian=0.18 degree.

Your stepper (at full step) with the belt reduction is 1.8/ (32/14)=0.787 degree per full step.
You will need a microstep setting of at least 8 (1600 steps per revolution) to achieve your resolution.

If you set your driver at 8 microsteps your 'step per unit' in the motor tuning page should be:
(1600 x32/14)/360= 10.16 steps per degree.

A suitable speed might be one rev per second or 360 degrees per second or 21600 degrees per minute.
Suggest an acceleration of 300.

Try it and see.

Craig

Thanks I gave those 2 files a test and it moved as expected.

I set the driver and the motor setting to the values you suggested. I worked correctly. It took 1:12 to rotate which works out to 300 degrees per minute.

I'd like to get higher speeds than that though.

Hi,
fine, then up the velocity, 21600 degrees per min is one rev per second, double it and see what happens.

When you have a rotary axis which has such wildly different numbers as these you can get into diffuculty.
If for instance you specify F=200 expecting the linear axes to travel at 200 inch/min then you'll be dissapointed,
the rotary axis will rotate at 200 degrees/min, less that one turn per min, and the linear axes will move glacially
slowly to stay synchronised.

In this circumstance the slowest axis determines the speed of all the rest.

Now imagine you you set F=20000 that would allow the rotary axis will go about 1 rev per second but the linear axes can
only go 350 inch/min and will that will limit the speed of the rotary axis to stay synchronised. Again its the slowest axis
that sets the pace.

Craig

Hi,
try a file with just rotary moves:

g0 a0
a270
a0
a270
a0
should move the a axis back and forth 3/4 turn at the max rate, about 360 degrees per second.

Now
g1 a0 f5000
a270
a0
a270
a0
What happens?

Craig

Thank I'll try just the A tonight.

What you are saying about the slowest axis makes sense. I'm not sure how to get around the huge difference in feedrates.

I watched some videos of commercial A axis and found a some sample code for setting them up. The feedrates were more in line with what I expected (they used 50, 100 and 200) in the videos, with good movement and rotation speeds.

I am curious how there mechanics work. I made mine from stuff I had lying around, so I understand I'm not going to get the same performance as a $4k+ professional tool. But they are still being accurate as they rotate. Is it all software?

To supplement Gaig's replies, the following should be of value.

What do i need to do to get my code running at a decent speed?

You will need to know what is the max velocity is for each of the axis.
 In a synchronised move the slowest axis determines the speed of all the rest.
So you are limited by the slowest max velocity.

One can use a  Stepper Caculator located in Members Doc's to find steps per unit and it
also gives additional info.

http://www.machsupport.com/forum/index.php/topic,16315.0.html

Assuming that the XYZ are tuned and represent reliable operation then you have the max
velocity in units per min. Now you need to know the same for an A axis ( rotary )
and it's nice be able to relate the deg/min (max feedrate) to the linear axes feedrate.

You tune a rotary similar to a linear axis as follows:
- Steps per degree is calculated.
- use a velocity ( deg per min) of 360 and accel of say 10
- double the velocity until the rotary skips, and reduce velocity by say 10%.
- now increase the accel, say 10, 400, 1600, 3200, etc and find where it skips
  for the max velocity found.
You have now know where the A axis skips for a your velocity and acceleration settings.

To relate the rotary to rpm just  manualy time ( or  measure rpm ) how long  it takes to make
 1 revolution, say over 4 revolutions. Do that for a few lower / different velocity settings below
the max velocity found.

The attached shows results of the above in a spread sheet.
Angular Motor Tuning shows an rpm value for the rotary.
Linear unit per Min at table RPM - Since the slowest axis will govern the max velocity that
can be used in a sychronized move this relates the linear axis to roatry axis velocities.
Say the max linear axes velocity is set at 60 inches per min and is represented by the yellow,
then max angular velocity for a  coded sychronized move should be restricted such that it doesn't
exceed the rotary table rpm.

You have what you have and if  not satisfactory then change the mechanics of the system.

RICH

I tried the just A code as recommended and it run nice and fast, the second file slowed it down to about 1/4 the speed.

I was thinking about this today. And I think what I want is my Feedrate for the A axis in revolutions per min. I am have a hard time switching my brain to degrees per minute.

At 21600 dpm, this is a feedrate of 60 rpm. And When i look at it that way it makes sense to me.

Is there a way to make mach go in rpm?

Hi,
what you are talking about is changing Machs Gcode interpreter which I don't think is possible, certainly
without major support/cooperation from NFS.

Even if you changed the DROs so it appeared that rotational axes appeared in units of per revolution,
all CAM programs still generate rotational axes in degrees.

I am have a hard time switching my brain to degrees per minute.

The short answer is reprogram your head!

Craig

The proper solution is to use G93 – Inverse Time Feed. Study up on it. You can find information about it in the Mill Gcode programming.pdf file in your Mach4/Docs folder.